The present disclosure relates generally to heart rate estimation and in particular to context-aware heart rate estimation.
Many individuals in the modern world want to become more physically fit. Such individuals may engage in a variety of fitness activities. One popular form of fitness activity involves aerobic exercise, such as running, cycling, swimming, or the like. During aerobic exercise, the individual's heart rate can be used as a key metric for determining whether the individual is exercising at appropriate intensity. For example, many experts recommend exercising with enough intensity to maintain the heart rate in a range from about 65-85% of an age-dependent maximum heart rate. Knowing one's heart rate in real time can therefore be helpful in maximizing the benefits of aerobic exercise.
Knowing one's heart rate can have other benefits as well. For instance, resting heart rate (the heart rate when the person is sitting or lying still) can be a general indicator of overall cardiovascular health. Heart rate can also be used, in combination with other data, as an indicator of energy expenditure, allowing the individual to better understand his or her personal metabolism.
One traditional way to determine an individual's heart rate during exercise involves counting pulses felt at a pulse point such as the wrist or neck. For example, the individual can place one or more fingers over a pulse point and count pulses while watching a clock for a prescribed number of seconds; the heart rate can be determined, e.g., by dividing the pulse count by the elapsed time, by counting for ten seconds and multiplying by six to compute beats per minute, or the like. This, however, generally requires the user to pause, or at least slow down, the activity long enough to find a pulse and a clock or timer, making it inconvenient and disruptive to the continuity of the activity.
To alleviate this inconvenience, various devices exist that can monitor a user's heart rate. One type of heart rate sensor includes electrodes placed near or over the heart. The electrodes can be, for example, incorporated into a chest strap that the user wears, and the chest strap can communicate with a device worn in a more convenient location, such as on the user's wrist. Chest straps, however, are generally uncomfortable to wear, and this may limit the range of situations in which a user is likely to use the device. Another type of heart rate sensor is a fingertip “pulse oximetry” sensor. These sensors are often used in clinical settings to measure both pulse (heart rate) and hemoglobin oxygenation saturation using photoplethysmography (“PPG”). However, these types of sensors are generally not reliable when the wearer is moving around, so they are not considered ideal for use during physical activity.